The objective of this research is to define in objective terms the steps leading to macrophage activation for tumor cell killing, and the regulation of this process. Specifically the role of lymphokine in the activation process will be explored. Evidence to date suggests that lymphokine may prime macrophages to respond to a second, triggering signal, rather than activate them fully. The role of prostaglandin E as a negative regulator of this process will be explored more fully. In addition, monoclonal antibodies will be used to probe the question of whether subpopulation, if they exist, behave differently in their response to activating stimuli.